Although raised a Tidewater aristocrat, Mason graduated from the University of Pennsylvania and, after studying law at the College of William and Mary, set up his practice in the Virginia back country. He served in the state legislature from 1826 to 1832 (except for 1827) and one term in the U.S. House of Representatives (1837–39) before being appointed in 1847 to fill an unexpired Senate term.

Reelected for terms beginning in 1849 and 1855, Mason allied himself closely with other states’-rights Southern Democrats in the Senate. With Abraham Lincoln’s election in 1860, Mason advocated Southern secession and resigned his Senate seat to join the Confederacy. He accepted appointment by Pres. Jefferson Davis to serve as Confederate commissioner to England. Accompanied by John Slidell, he sailed for England aboard the British ship “Trent.” The “Trent” was captured at sea by a U.S. naval vessel, and the two Confederate diplomats were imprisoned for two months in Boston.

The Trent Affair nearly caused a severance of diplomatic relations between the U.S. and Great Britain. But on Jan. 1, 1862, Pres. Lincoln ordered the release of Mason and Slidell, and the two emissaries made their way to Europe. In England, however, Mason was able to make little progress in winning official support for the Confederate cause.

Mason did not return to North America until 1866, and he stayed in Canada—afraid of being arrested as an important official of the defeated Confederacy—until 1868. Following Pres. Andrew Johnson’s second proclamation of amnesty in 1868, however, Mason returned to Virginia, where he lived his final years.